The present invention relates to facsimile transmission control systems. More particularly, the present invention is directed to a facsimile transmission control system capable of outputting an appropriate response when a post-message instruction signal is received without decoding any lines of image information.
Conventional G3 facsimile transmission control procedures are standardized in the CCITT (Consultative Committee for International Telegraph and Telephone) recommendation T.30. According to this message receiving procedure, there are two possible cases where a post-message instruction signal is received without decoding any lines of image information. One case is that the post-message instruction signal is received without correctly decoding any lines of image information due to transmission errors, and the other is that the post-message instruction signal is retransmitted by a counterpart terminal since the counterpart terminal is not able to receive a MCF (Message Confirmation) signal correctly due to noise or the like.
Different responses must be given in these two cases. In the former case, a RTN (Retransmission) signal must be returned to request retransmission of the image information, whereas in the latter case, the same response as the last communication, e.g., the MCF signal, must be returned. However, to make such judgment is very difficult.
In contrast to the above-mentioned cases, Unexamined Japanese Patent Publication No. 130667/1989 proposes that a RTN signal is returned in both of the two cases. However, this system is time-consuming in terms of procedure for taking care of the latter case because the RTN signal is returned instead of the MCF signal. In addition, many facsimile machines retransmit the page concerned when the RTN signal is received. Thus, the counterpart terminal has to receive the same page twice, which is a waste of paper.
Further, Unexamined Japanese Patent Publication No. 61470/1992 proposes that an instruction signal original to a transmitting-side facsimile machine is sent before sending image information so that the counterpart terminal can be informed of the fact that the content to be next sent is a high-speed image information signal. However, this system is only valid in the original mode, thereby not being used for communications with machines of different origin.